A Method for Approximating Surface Elevation From a Shore Mounted X-Band Radar With a Low Grazing Angle
- Charles E. Greenwood (University of the Highlands and Islands) | James Morrison Angus Murray (University of the Highlands and Islands) | Arne Vogler (University of the Highlands and Islands)
- Document ID
- International Society of Offshore and Polar Engineers
- The 27th International Ocean and Polar Engineering Conference, 25-30 June, San Francisco, California, USA
- Publication Date
- Document Type
- Conference Paper
- 2017. International Society of Offshore and Polar Engineers
- Radar, Surface Elevation, AWAC, Wave Buoy, Real-time, Wave Measurements
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- 18 since 2007
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X-band radar provides a spatial backscatter results over a large area. This shows wave features to be clearly visible over a large area providing an advantage over standard in situ measurements. This paper suggests a new method of quantifying surface elevation in an almost real-time method by applying a second order Stokes waves in shadow regions (troughs). The initial results show the artificial wave trough method having an improvement in phase and magnitude when compared to independent in situ measurements. This method provides a better representation of the surface elevation. Once refined, the real time surface elevation can be used as boundary conditions for a short-term wave-forecasting model.
The use of X-band radar as a method of wave and current measurements has been around for a number for years (Alpers & Hasselmann, 1982; Young, Rosenthal, & Ziemer, 1985). This is due to the interaction between the sea's surface and electromagnetic wave that allows wave images to be collected over an area of several kilometers in all directions. Previously, these images were referred to as sea clutter as they are a byproduct of a ships navigation radar. A high-resolution spatial and temporal map of wave condition and surface currents can be created when an X-band radar is optimized to receive this clutter information.
The applications of X band radar to measure waves and currents is common, however, in a few cases this has been extended measure bathymetry. (Ludeno et al., 2015; Tenthof van Noorden, 2015; Trizna, 2001) and uses a dispersion relation filter to track the change in wave profiles as then interact with the seabed.
A large number of studies had originally focused on the analysis of radar data to extract wave spectra (Borge, Hessner, Jarabo-Amores, & de la Mata-Moya, 2008; Gangeskar, 2000; J. C. Nieto Borge, Reichert, & Dittmer, 1999; Seemann, Ziemer, & Senet, 1997). This normally uses the Signal to Noise Ratio (SNR) and a three dimensional dispersion relation filter with additional measurement coming from in situ wave sensors i.e. wave buoy or a ship's inertial measurement unit (IMU). This provides a good agreement when compared against standard wave measuring sensors. The calculated spectra however, is only capable to produce an output over a given period of time and for a given area. This provides good phase-averaged wave quantification but omits phase-resolving feature that are important for short-term wave predictions. In terms of resource assessment, the radar-derived spectra provides a low spatial and temporal resolution map, this remains a substantial advantage when compared to traditional 1-dimensional wave recordings from fixed locations.
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